All you can do is put things in front of the sound,Less is More.
In the 90s i had a pr of the MG3a like you an Windell at Magnepan told me there was no better way to get good sound,To day thay have found the crossover that thay use is the only way to go ... Ok for there new MG1.7s an other .7 Maybe...Your setup work vary good with the MG3a,s...Your on the right path i think,just get caps you like an your there...

The photo show a nice 6db/oct filter, with an 'nice' resistor coming from nowere...
6db/oct is the most artistical soluiton, on the paper it gives the perfect results...
Reality is completly different : the two speakers must match in many areas, having the same 'tone', the same phase shift, the same impulse response, the same power handling...
... on three octaves at least.

If no, then ... I experienced so many failures in the last 30years that I will not review them.
Basically, there is no way to obtain high level of sound with a 6dbct filter, in respect with a good impulse response and stable stereo image. Few succeded, I admire them !

About MGIII : only having a look to the impulse response of the bass and mid panels of the MGIII show that ther is a total incompatibility. Sorry for the Magnepan staff for whom i've got the highest respect.
The medium pannel is far away quicker than the low panel.

12db gives acceptable results, 18db/oct is 'better in impulse response, but i prefered the less precise but more rich sound given by the 12db/oct.

Well wheres my Rs........12db works for me...I have a pr of 3a here now got them for free, geting them out of a guys house, thay went or he went! An dont think thay sound good with anyset up i have,maybe the R tweeter with my Acoustat M3s...but have not even done that goodluck....

Aarghh...
I m trapped.
i don t know the latest mgs, i can only assume that the impulse response of the low frequency pannel is closer to the mid pannel. Mg people know these pannels like their own children and they found a way to quicken the low pannel...
Basically the big advantage of the mg s is that low and mid pannel use the same mylar film. So at least the 'tone' is the same.
When writing a out my attemts about tuning 6db/oct filters, i was maily thinking about traditional speakers. 20years ago i sweared only by 6db, listening tests brang me bagk o reality...
cheers
mathieu